In a silver halide photographic element, a color image is formed when the element is exposed to light and then subjected to color development with a primary aromatic amine developer. Color development results in imagewise reduction of silver halide and production of oxidized developer. Oxidized developer reacts with one or more incorporated dye-forming couplers to form an imagewise distribution of dye.
In any polychromatic chromogenic photographic material it is desirable that the dyes so formed should have certain properties. For instance the dyes should be bright in color with very little secondary absorption so that good color reproducibility is obtained. For yellow dyes in particular, color purity is enhanced by ensuring that the absorption maximum of the dye is well separated from that of the magenta dye, and hence yellow dyes that absorb at shorter wavelengths are advantageous. Acetanilide-based yellow dye-forming couplers have been found to provide desirable dye hues. The dyes that are formed by any color coupler during processing have a tendency to fade over time as a result of exposure to light, heat, humidity and oxygen. Since the three image dyes may not fade at the same rate, an apparent change in image color may result. It is thus paramount that the formed photographic dye images should be resistant towards fading by heat, humidity and light.
When the dye images are formed in silver halide photographic materials from the combination of oxidized developer and an incorporated coupler, certain restrictions are placed on the properties of the coupler. For instance, the coupler should produce a dye which has the aforementioned desirable properties and the efficiency of the dye-forming reaction must be high. Additionally, the coupler must be easily dispersible, must itself be resistant towards the deleterious effects of light, heat and humidity, and must have a low propensity to form fog.
Acetanilide-based yellow dye-forming couplers of the general structures described in this invention are well known in the art of photography. It is also well known in the art of coupler chemistry that the incorporation of specific functionalities into the molecule can enhance features such as coupling reactivity or high image dye light stability. Another well-proven route to improve image dye light stability is to incorporate certain stabilizing addenda into the coupler dispersion. Such stabilizing addenda can be used alone or in combination. Compounds which have been disclosed as stabilizers for yellow image dyes include substituted phenolic and blocked phenolic compounds, including heterocyclic phosphorous compounds (U.S. Pat. No. 4,749,645), phenolic thiane derivatives ((EP 0 310 551) and substituted bisphenols (UK 1,267,287), among which mono-blocked derivatives have been shown to be especially advantageous (U.S. Pat. No. 4,782,011). The use of substituted bisphenols and blocked bisphenols as light stabilizers for yellow image dyes has additionally been described in detail in, e.g., DE 4,307,439, DE 4,320,828, EP 0 508 398, EP 0 538 862, U.S. Pat. Nos. 5,294,530, 5,426,021, 5,441,855, 5,441,861, 5,466,569, 5,891,613, and WO 91/008,515. Further advantages are claimed for the combination of such bisphenol stabilizers with certain spirocyclic compounds in U.S. Pat. No. 5,567,578. U.S. Pat. No. 5,284,742 describes the combination of certain yellow couplers with alkylated quinone type stabilizers and phenolic stabilizers for improved color reproduction and light stability. U.S. Pat. No. 5,091,294 describes the combination of certain yellow couplers with thiane stabilizers for improved color reproduction and light stability. EP 0 310 552 describes the use of thiane derivatives combined with yellow dye-forming couplers and phenolic antioxidants for improved light stability. U.S. Pat. No. 5,935,773 describes the combination yellow couplers with cyclo-dextrans and phenolic stabilizers for improved color reproduction and light stability. However, there remains a continuing need to seek coupler formulations with improved performance because, quite often, one or more of the other desirable properties of the photographically formed dye (such as its hue or its efficiency of formation) can be affected adversely by these artifices.
U.S. Pat. Nos. 5,017,465 and 5,082,766 and German Published Patent Application DTOS 4,307,194 describe the use of certain stabilizers with pyrazoloazole magenta dye forming couplers to improve their dye stability. One class of stabilizers which is disclosed includes compounds of the following structure: ##STR2##
wherein A represents a group of non-metal atoms necessary to complete a 5-membered to 8-membered nitrogen-containing ring and R.sup.0 represents an aryl group or a heterocyclic group. Preferred compounds of such formula as described in U.S. Pat. No. 5,017,465 include compounds wherein A represents the atoms necessary to complete a thiomorpholine 1,1-dioxide group and where R.sup.0 represents an alkoxy substituted phenyl group. Such compounds are believed to stabilize by acting as singlet oxygen quenchers. U.S. Pat Nos. 5,236,819 and 5,561,037 disclose that the light stability of the image dyes from such cyclic azole magenta couplers can be further improved by the use of a combination of stabilizers which include thiomorpholine dioxide compounds, U.S. Pat. Nos. 5,561,037 disclosing the use of substituted sulfonamido phenyl compounds in such combinations. The utility of thiomorpholine dioxide stabilizers in relation to 2-equivalent pyrazolone magenta couplers is also disclosed in U.S. Pat. Nos. 5,491,054 and 5,484,696.